Acquired Intangible Assets and Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization of below market leases	$ 2,300	$ 2,300
Expected average remaining lives of acquired below market leases (in years)	7 years
Amortization of intangible assets	$ 41,841	17,379
Acquired above-market leases
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives (in years)	4 years 4 months 24 days
Acquired in-place lease value
Finite-Lived Intangible Assets [Line Items]
Expected average remaining lives (in years)	8 years 2 months 12 days
Amortization of intangible assets	$ 13,700	$ 11,600
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)	7 years 7 months 6 days
Tenant relationship value
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 15,900
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)	11 years 1 month 6 days
Trade name
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 500
Weighted average remaining contractual life for acquired leases excluding renewals or extensions (in years)	3 years 6 months